Relaxation of abnormal rolls in planarly aligned electroconvection

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Rudroff, Stefan ; Frette, Vidar ; Rehberg, Ingo:
Relaxation of abnormal rolls in planarly aligned electroconvection.
In: Physical Review E. Bd. 59 (1999) Heft 2 . - S. 1814-1820.
ISSN 1550-2376
DOI: https://doi.org/10.1103/PhysRevE.59.1814

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Abstract

Experimental results on electroconvection in a planarly aligned nematic liquid crystal are reported. Special emphasis is given to an optical technique for investigating abnormal rolls, which are characterized by a twist in the director field. The order parameter of the twist is measured by ellipsometry. We have also carried out a numerical investigation of the optical setup using a transfer-matrix method. The relaxation time of the twist has been measured and compared to theoretical predictions. In particular, it is found that the twist in the abnormal rolls forces the director field at the glass surface to turn away from its preferred direction (weak anchoring). This distortion in the anchoring of the liquid crystal relaxes one order of magnitude slower than theory predicts for relaxation processes driven by elastic forces in bulk.